1. Field of the Invention
The present invention relates to RFID (Radio Frequency Identification) systems and, in particular, to near field antennas for such systems configured to selectively communicate with a targeted RFID transponder from among a group of adjacent transponders.
2. Description of Related Art
RFID technology is rapidly becoming essential to not only accurately manage assets and inventory, but also in a variety of other practical applications. With respect to inventory applications, RFID tags, also known as transponders, are being used to count and identify inventory in retail stores, warehouses, shipping containers, and the like, to allow for more accurate bookkeeping and ordering of replacement or replenishment goods. Moreover, it has been determined that many other applications for RFID technologies are becoming increasingly beneficial and/or economical. For example, RFID transponders are being used in security applications to grant individuals access to secure areas. RFID transponders are also being used in vehicles to pay tolls while maintaining vehicle speeds. Further, RFID transponders are even being implanted in pets to allow for accurate identification of a pet in the event that the pet is lost. As such, RFID technology is becoming ubiquitous in a wide variety of applications, and new applications for the technology are being developed continuously.
A conventional RFID system provides for wireless data acquisition from/to transponders to/from a transceiver. In various applications, the transponders may be active (e.g., battery-powered, battery-assisted, or battery supported) or passive (e.g., activated by an RF field). A conventional transponder includes an antenna that facilitates the reception of communications from the transceiver. In order to encode (e.g., read, write), the transceiver through an antenna of the transceiver exposes the transponder to a radio frequency (RF) electromagnetic field or signal. In the case of a passive UHF transponder, the RF electromagnetic field energizes the transponder and thereby enables the transponder to respond to the transceiver by re-radiating the received signal back and modulating the field in a well-known technique called backscattering. In the case of an active transponder, the transponder may respond to the electromagnetic field by transmitting an independently powered reply signal to the transceiver. In this manner, various applications for RFID technology may be implemented.
Some RFID applications utilize transponders that may be encoded prior to utilization within a system. In this regard, a transponder may be encoded by communicating commands and/or data to a transponder such as, for example, a unique identifier. The transponders may be encoded in a number of ways. In some instances, a printer may be configured with a specialized printhead or other apparatus (e.g., a printer-encoder) that may be utilized to encode the transponders. The encoding process can involve magnetic coupling the transponder to the printer-encoder through an antenna of the printer-encoder such that commands or data are transmitted to the transponder to facilitate the encoding process. Some conventional printer-encoders can encode transponders that are affixed to or embedded on a media, such as a smart label or a tag. When the media passes through the printer-encoder, the printer-encoder is configured to encode the transponders affixed to the media such that the transponders may be later used in connection with other RFID systems and applications.
However, in some instances, errors in the encoding process (e.g., improperly encoded transponders or encoding failures) can occur due to the variations of the justification and type of transponders to be encoded. Justification refers to the location of the transponder relative to the antenna or other reference point of a printer-encoder. The encoding errors largely arise from non-uniform location or orientation of the transponder on the media received by a printer-encoder. As a result, the location of the transponders relative to the antenna of the printer-encoder may be unpredictable, and the electromagnetic field generated by the antenna of the printer-encoder may not be effective for encoding of the transponders. As such, it may be desirable to develop and implement a system and antenna that can account for the unpredictability of the positioning of a transponder relative to the near-field coupling device.